The present invention relates to a thermal recording apparatus such as a thermal facsimiles recording or the like and in particular to an improvement of the recording head for the thermal recording apparatus in respect of durability.
In general, the thermal recording apparatus comprises a plurality of heat-generating resistance elements adapted to be selectively applied with pulse-like current, wherein Joule heat as generated is transmitted to a recording medium such as a paper applied with a layer of material which responds to the heat and changes the color thereof in contrast to the background color thereby to form visible information recorded thereon. The pulse-like drive current is controlled in dependence upon the information signal so that the visible information may be recorded on the medium in accordance with the information signal.
In the thermal recording apparatus, a unit which comprises a plurality of heat-generating resistance elements, a plurality of electrodes for applying selectively current to the heat-generating resistance elements and a plurality of lead wires connected to the electrodes is referred to as a recording or printing head.
As is known in the art, when a direct current or d.c. voltage is applied to a conductor having a high resistivity through lead wires having a low resistivity, metal ions are diffused from the lead wire at which negative potential is applied into the conductor at the boundary region therebetween, which region will become discolored and deteriorated in quality after long use.
It is known that undesirable deteriorating phenomenon will also occur in the recording or printing head of the thermal recording apparatus at the region in the vicinity of the boundary between the heat-generating resistance elements and the electrodes for applying a negative potential to the resistance elements. In this connection, the deterioration procedes rapidly in the case of the recording head since the heat-generating resistance elements are heated at a high temperature. As an attempt to obviate the deterioration, it is known to select appropriate materials for the electrodes and the resistance elements. However, such attempts are necessarily accompanied with an increased expenditure. Further, the recording head manifactured in this way is unsatisfactory in respect of the resistance to repeated thermal cycles.